Leetcode -- Minimum Window Substring

 #include <iostream>  
 #include <unordered_map>  
 #include <climits>  
 using namespace std;  
 class Solution {  
 public:  
  string minWindow(string S, string T) {  
   if(S.empty()) {  
    return "";  
   }  
   unordered_map<char, int> expectedToFind;  
   unordered_map<char, int> hasFound;  
   for(int i = 0; i < T.length(); ++i) {  
    expectedToFind[T[i]]++;  
   }  
   int minLength = INT_MAX;  
   int minStart = 0;  
   int minEnd = 0;  
   int count = 0;  
   for(int start = 0, end = 0; end < S.length(); end++) {  
    if(expectedToFind[S[end]] > 0) {  
     hasFound[S[end]]++;  
    }  
    if(expectedToFind[S[end]] > 0 && hasFound[S[end]] <= expectedToFind[S[end]]) {  
     count++;  
    }  
    if(count == T.length()) {  
     while(expectedToFind[S[start]] == 0 || hasFound[S[start]] > expectedToFind[S[start]]) {  
      if(hasFound[S[start]] > expectedToFind[S[start]] ) {  
       hasFound[S[start]]--;  
      }  
      start++;  
     }  
     int wLen = end - start + 1;  
     if(wLen < minLength) {  
      minLength = wLen;  
      minStart = start;  
      minEnd = end;  
     }  
    }  
   }  
   return count == T.length() ? S.substr(minStart, minEnd - minStart + 1): "";  
  }  
 };  
 int main(int argc, char *argv[])  
 {  
  Solution s;  
  std::cout << s.minWindow("a", "a") << std::endl;  
  return 0;  
 }